Method of manufacturing a cathode plate, and a cathode plate

ABSTRACT

A method of manufacturing a cathode plate ( 1 ) that is used in the electrolytic cleaning and recovery of metals, the cathode plate being at least partly manufactured of stainless steel and the surface of the cathode plate being treated in at least one stage, whereby the cathode plate is formed by cutting it from a solid plate-like material ( 2 ), whereby, essentially before cutting ( 4 ) the cathode plate to shape, at least part of the surface constituting the cathode plate is subjected to a mechanical treatment ( 3 ) to improve the adhesion properties of the surface. The invention also relates to the cathode plate.

This is a national stage application filed under 35 USC 371 based onInternational Application No. PCT/FI2008/050055 filed Feb. 13, 2008, andclaims priority under 35 USC 119 of Finnish Patent Application No.20070125 filed Feb. 13, 2007.

The present invention relates to a method of manufacturing a cathodeplate that is used in the electrolytic cleaning and/or recovery ofmetal, and to a cathode plate.

BACKGROUND OF THE INVENTION

In the electrolytic cleaning and recovery of metals, the surface qualityof the cathode plate is important. By affecting the adhesion propertiesof the surface, a cathode plate of a better quality is obtained. In theelectrolytic cleaning of copper, the copper that is dissolved in theelectrolyte from copper anodes precipitates as pure copper, by means ofan electric current, on the surface of the cathode plate, from where itis typically removed mechanically in the form of a copper plate. In therecovery of copper, copper precipitates on the cathodes directly fromthe electrolytic solution. The cathodes are generally called permanentcathodes, because they can be re-used subsequently. It is well-known touse stainless steal as the material of the cathode plate. Generally,acid-proof steel 316 L is used, having a surface quality of 2B, wherebythe R_(a) value describing the roughness of the surface is within arange of 0.3-0.6 μm. Typically, the surface mentioned above is obtained,when the steel plate working as the cathode is cold-rolled, annealed,etched in an acid bath, and subjected to dressing. In etching anddressing, the grain boundaries of the steel open, whereby microscopicgrooves and canyons are formed on the surface of the steel plate, andthe electrolytically coated metal is able to grow in and attach to thesegrooves and canyons. In use, however, the surface of the steel plateundergoes wear, contamination and changes, whereby the surface must betreated by brushing and grinding. In terms of process technology,manufacturing the surface of the cathode plate by etching and dressingis quite challenging, and an unacceptably short etching time can easilydestroy the quality of the surface so as to become unsuitable for theelectrolytic coating.

Publication FI 68430 B, for example, discloses the use of stainlesssteel as material for cathodes. Regarding the material, the publicationdescribes in detail the AISI 316L steel, which has a surface treatmentknown as Standard 2B. The publication mentioned above states that thematerial in question is advantageous, as a sufficient fixing adhesion isprovided between the steel plate and the copper so that the copper doesnot detach of its own accord before the actual releasing phase. The useof stainless steel as the material for cathodes is also disclosed inpublication U.S. Pat. No. 6,485,621 B. Publication US 2006/0201586 A1discloses a permanent cathode that is used in the electrolytic refiningof metals, consisting of duplex steel containing a small content ofnickel, or of steel grade “304”. The publication goes on to describethat the surface of the cathode plate is treated to improve its adhesionproperties. The publication presents a surface treatment for improvingthe adhesion properties of the cathode surface, such as a mechanicaltreatment, e.g. grinding, to change the hardness of the surface, andetching. Furthermore, the publication suggests that the cathode surfacebe slotted to improve the above-mentioned properties.

SUMMARY OF THE INVENTION

This invention relates to the method of manufacturing a cathode platethat is used in the electrolytic cleaning and recovery of metals, and toa cathode plate that is manufactured by the method. In particular, thepurpose of the invention is to provide a solution to the manufacture ofcathode plates, whereby the cathode plate is made by cutting it from asolid plate-like material, whereby before cutting the cathode plate toshape, at least part of the surface forming the cathode plate issubjected to a mechanical surface treatment to improve the adhesionproperties of the surface.

The essential features of the invention are disclosed in the appendedclaims.

The invention relates to the method of manufacturing a cathode platethat is used in the electrolytic cleaning and/or recovery of metals, thecathode plate being at least partly manufactured of stainless steel, andthe surface of the cathode plate being treated in at least one stage,whereby the cathode plate is formed by cutting it from a solidplate-like material, whereby essentially before the cathode plate is cutto shape, at least part of the surface constituting the cathode plate issubjected to a mechanical surface treatment to improve the adhesionproperties of the surface. In the mechanical surface treatment, groovesare then formed on at least part of the surface of the cathode plate,being in a horizontal direction with respect to the direction ofsuspension of the cathode plate. According to an embodiment of theinvention, the mechanical surface treatment is carried out with at leastone surface treatment member by immersing it in the surface of theplate-like material at a right angle, while the surface moves, wherebythe surface treatment member is a brush and/or a grinding apparatus, forexample. By accurately directing to the surface, to a desired spot onthe surface, a mechanical surface treating device, a desired roughnesslevel of the surface is achieved, preferably improving the adhesionproperties of the surface. When the grooves on the surface of thecathode plate are in a horizontal direction with respect to itsdirection of suspension, the vertical force of the grooves keeps theprecipitated metal plate attached to the cathode, while the cathodehangs. The horizontal grooves on the surface of the cathode plate forman advantageous surface of adhesion for the metal that is precipitatedon the surface at the beginning of the coating cycle, in particular. Ifthe grooves were in a vertical direction, their adhesive power would notbe as good as that of the horizontal grooves, and the cathode would mostlikely drop off the metal plate too early. When detaching the cathodeplate, the cathode is generally bent, whereby the separating force isexerted sideward and, in that case, the horizontal grooves do not impedethe detachment. In terms of manufacturing techniques, the method isadvantageous, as the individual cathode plates do not need to be treatedseparately.

According to an embodiment of the invention, the grooves are formed sothat they extend over the entire surface of the cathode plate, wherebythey improve the adhesion of the precipitated metal throughout thesurface. According to a preferred embodiment of the invention, in themechanical surface treatment, the grooves are formed so that their depthin the cathode plate is preferably 5 to 10 μm, and so that the distancebetween adjacent grooves is preferably 10 to 30 μm. According to anembodiment of the invention, the mechanical surface treatment is carriedout on both sides of the cathode plate, whereby the adhesion of themetal layer that is precipitated on both sides of the cathode plate alsoimproves. According to the invention, the surface of the plate-likematerial is possibly rolled into a desired thickness before themechanical surface treatment. According to an example of the invention,the surface of the plate-like material is subjected to dressing tostraighten the plate before cutting the cathode plate. According to theinvention, the cathode plate is at least partly formed of a plate-likematerial that comprises austenitic steel and/or ferritic-austeniticsteel. By means of the surface treatment according to the invention, acathode plate is provided, the R_(a) value of its surface preferablybeing 0.3-0.6 μm, which is advantageous for the adhesion. The cathodeplate manufactured by the method according to the invention is apermanent cathode, for example, i.e., it can be re-used.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the equipment according to the invention is describedwith reference to the appended drawings, in which:

FIG. 1 is a basic figure of the manufacturing method of the cathodeplate according to the invention,

FIG. 2 is a basic figure of the finished cathode plate.

DETAIL DESCRIPTION OF THE INVENTION

FIG. 1 shows the method according to the invention for manufacturing theelectrolytic plate or cathode plate 1 that is used in the electrolyticcleaning and recovery of metals. The cathode plate is made of plate-likematerial 2, which is stainless steel, such as austenitic orferritic-austenitic steel and, according to the method of the invention,the surface that forms the cathode plate is treated in at least onestage to affect the adhesion properties of the surface to improve thepermanence of the metal layer that precipitates on the surface. Thecathode can be used as a permanent cathode, i.e., it can be re-usedsubsequently. The cathode plate 1 is formed by cutting it from the solidplate-like material 2, whereby, essentially before cutting 4 the cathodeplate to shape from the plate-like sheet metal, a mechanical surfacetreatment 3 is carried out on at least part of the surface that formsthe cathode plate to improve the adhesion properties of the surface.When the roll of plate-like material 2 moves, a mechanical surfacetreatment member, such as a brush and/or grinding apparatus or the like,is preferably directed to its surface in a perpendicular direction sothat it digs into a desired depth on the surface of the plate-likematerial. It is important to be able to adjust the mechanical surfacetreatment member to a desired height and to a desired spot on theplate-like material. In the mechanical surface treatment 3 according tothe invention, grooves 5 are formed on at least part of the surface thatforms the cathode plate before the stage of cutting 4 to shape thecathode plate 1 from the plate-like material, the grooves 5 being in ahorizontal direction with respect to the direction of suspension of thecathode plate. The grooves are formed in the same direction as thedirection of movement of the plate-like material. The direction ofsuspension of the cathode plate refers to the direction, in which ithangs with respect to a hanger 6 in a tank designed for electrolyticcleaning or recovery, for example.

According to the example of this invention, the grooves 5 are formed onthe plate-like material 2 so as to exist on both sides of the finishedcathode plate 1 so that the surface of the cathode plate is evenlyslotted. According to the example, in the surface treatment of thecathode plate 1, the grooves are formed so that their depth in thecathode plate is 5-10 μm, e.g., 8 μm, and the distance between adjacentgrooves is about 10-30 μm, e.g., 15 μm. The R_(a) value of the surfacethat is formed on the cathode plate, which is made according to theinvention, is preferably 0.3-0.6 μm, which is preferable for theadhesion. Before the mechanical surface treatment, the surface of theplate-like material is rolled to a desired thickness to correspond tothe optimal thickness of the cathode plate, which hangs on the hanger 6that is used in the electrolytic cleaning or recovery, and so that thecathode plate is mechanically strong enough to endure the stress, whichis inflicted on the cathode by the detachment of the metal layer, andwhereby the metal plate is easy to detach. When so needed, the finishedplate-like material can be subjected to dressing 7 before the cathodesare cut 4 to shape, whereby the plate is straightened to facilitatecutting.

It is obvious to those skilled in the art that the various embodimentsof the invention are not limited to the examples presented above but canvary within the scope of the appended claims.

1. A method of manufacturing a cathode plate (1) that is used in theelectrolytic cleaning and/or recovery of metals, the cathode plate beingmanufactured at least partly of stainless steel, and the surface of thecathode plate being treated in at least one stage, characterized in thatthe cathode plate is formed by cutting it from a solid plate-likematerial (2), whereby essentially before cutting (4) the cathode plateto shape, at least part of the surface that forms the cathode plate issubjected to mechanical surface treatment (3) to improve the adhesionproperties of the surface when in the mechanical surface treatment,grooves (5) are formed on at least part of the surface of the cathodeplate (1), the grooves being in a horizontal direction with respect tothe direction of suspension of the cathode plate.
 2. A method accordingto claim 1, characterized in that the mechanical surface treatment (3)is carried out with at least one surface treatment member by immersingit in the surface of the plate-like material (2) at a right angle, whilethe surfaces moves.
 3. A method according to claim 2, characterized inthat the surface treatment member is a brush and/or a grindingapparatus.
 4. A method according to claim 1, characterized in that thegrooves (5) are formed so as to extend over the entire surface of thecathode plate.
 5. A method according to claim 1, characterized in that,in the mechanical surface treatment (3), the grooves (5) are formed sothat their depth in the cathode plate (1) is 5 to 10 μm.
 6. A methodaccording to claim 1, characterized in that, in the mechanical surfacetreatment, the grooves (5) are formed so that the distance betweenadjacent grooves is 10 to 30 μm.
 7. A method according to claim 1,characterized in that the mechanical surface treatment is performed onboth sides of the cathode plate.
 8. A method according to claim 1,characterized in that the surface of the plate-like material (2) isrolled into a desired thickness before the mechanical surface treatment.9. A method according to claim 1, characterized in that dressing (8) iscarried out on the surface of the plate-like material (2) to straightenthe plate before cutting the cathode plate.
 10. A method according toclaim 1, characterized in that the cathode plate (1) is at least partlyformed of plate-like material (2) that comprises austenitic and/orferritic-austenitic steel.
 11. A cathode plate (1) that is used in theelectrolytic cleaning and/or recovery of metals, the cathode plate atleast partly comprising stainless steel, and the surface of the cathodeplate being treated in at least one stage, characterized in that thecathode plate is formed by cutting it from a solid plate-like material(2), whereby, before cutting the cathode plate to shape, at least partof the surface constituting the cathode plate (1) is subjected to amechanical surface treatment (3) to improve the adhesion properties ofthe surface when in the mechanical surface treatment, grooves (5) areformed on at least part of the surface of the cathode plate (1), thegrooves being in a horizontal direction with respect to the direction ofsuspension of the cathode plate.
 12. A cathode plate according to claim11, characterized in that the Ra value of the surface of the cathodeplate is 0.3-0.6 μm.
 13. A cathode plate according to claim 11,characterized in that the cathode plate at least partly comprisesaustenitic and/or ferritic-austenitic steel.
 14. A cathode plateaccording to claim 11, characterized in that the depth of the grooves(5) in the cathode plate is 5-10 μm.
 15. A cathode plate according toclaim 11, characterized in that the distance between adjacent grooves(5) on the cathode plate is 10-30 μm.
 16. A cathode plate according toclaim 11, characterized in that the cathode plate is a permanentcathode.